TSH may be low (primary hyperthyroidism) or high (secondary hyperthyroidism) In subclinical hyperthyroidism, T3 and T4 are normal but TSH is low · Laboratory · Primary hyperthyroidism · Intrinsic thyroid gland abnormality producing excess T4 · High free T4, low TSH, normal TRH stimulation test Secondary hyperthyroidism ·

April 8, 2024 - In primary hyperthyroidism, TSH levels are usually low because the pituitary gland reduces TSH production in response to high thyroid hormone levels. In contrast, free levels of T4 or T3 are high. This inverse relationship between thyroid hormones and TSH is a key indicator of primary hyperthyroidism. Conversely, in secondary hyperthyroidism, excessive pituitary gland production elevates the TSH levels...

Primary hyperthyroidism (also called “thyrotoxicosis”) is caused by: ... Secondary hyperthyroidism may be attributed to an over-stimulation of the thyroid.

May 1, 2023 - In primary hyperthyroidism, the thyroid produces large amounts of T3 and T4, which, through negative feedback inhibition, suppress TSH secretion from the anterior pituitary. In primary hypothyroidism, the thyroid produces insufficient amounts of T3 and T4, which leads to loss of negative feedback inhibition and increased production of TSH from the anterior pituitary. In secondary hyperthyroidism, the anterior pituitary produces large amounts of TSH, which, in turn, stimulates the thyroid follicular cells to secrete thyroid hormones in excessive amounts.

September 27, 2025 - The key difference between primary and secondary hyperthyroidism lies in their origin: primary hyperthyroidism stems from thyroid gland dysfunction (most commonly Graves' disease), while secondary hyperthyroidism results from pituitary or hypothalamic disorders causing excessive TSH production.

Hyperthyroidism refers to overactivity of the thyroid gland leading to excessive production of thyroid hormones. Thyrotoxicosis refers to the clinical effects of unbound thyroid hormones, whether or not the thyroid gland is the primary source. Secondary hyperthyroidism due to pituitary adenomas, thyroiditis, iodine-induced hyperthyroiditis, and treatment of children and pregnant or lactating women are not covered in this review.

Primary hyperthyroidism relates to the thyroid gland producing large amounts of hormone due to either uncontrolled growth of hormone-producing functional tissue or by way of an autoimmune process that interferes with the normal feedback control. Secondary hyperthyroidism may be attributed to an over-stimulation of the thyroid.

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June 28, 2024 - Primary hyperthyroidism: the pathology is within the thyroid gland. Secondary hyperthyroidism: the thyroid gland is being stimulated by excessive thyroid-stimulating hormone (TSH) in the circulation.

June 8, 2020 - A high TSH level indicates that the thyroid gland is not making enough thyroid hormone (primary hypothyroidism). The opposite situation, in which the TSH level is low, usually indicates that the thyroid is producing too much thyroid hormone ...

Her past medical history is significant for asthma that is well controlled with her rescue inhaler. Her laboratory studies demonstrate elevated levels of thyroid stimulating hormone. (Hashimoto thyroiditis) ... primarily due to thyroid disease (primary hypothyroidism) but can be caused by secondary ...

Primary hyperthyroidism: low TSH, raised fT4 and fT3 · Secondary hyperthyroidism (e.g.

July 9, 2025 - The McMaster Textbook of Internal Medicine is the first Canadian textbook of internal medicine developed at McMaster University, the birthplace of problem-based learning (PBL) and evidence-based medicine (EBM). It uses GRADE criteria to assess the quality of evidence.

Primary hyperthyroidism is due to thyroid pathology. The thyroid is behaving abnormally and producing excessive thyroid hormone. Secondary hyperthyroidism is due to pathology in the hypothalamus or pituitary.

May 26, 2014 - Primary hyperparathyroidism is diagnosed by laboratory tests. These indicate high-circulating levels of PTH, hypercalcemia and low blood phosphorous, as well as calcium in the urine.

September 18, 2024 - Investigations: corrected calcium, serum PTH (high in primary, low in malignancy), vitamin D, U&Es; imaging includes DEXA scan, renal tract ultrasound, neck ultrasound, and nuclear imaging.

When hyperthyroidism is associated with lesions of the pituitary gland or the hypothalamus, it is considered secondary and tertiary hyperthyroidism respectively. In comparison to primary hyper thyroidism, these clinical conditions are extremely rare (< 1% of hyperthyroidism).

September 16, 2024 - Low TSH: due to negative feedback on the pituitary/hypothalamus. ... Secondary hyperthyroidism involves stimulation of the thyroid gland by excessive thyroid-stimulating hormone (TSH).